Covering wood with resistant coatings



Patented Apr. 19, 1938 UNITED v STATES COVERING WOOD WITH RESISTANT COATINGS Wilhelm Otto Maisch, Stuttgart, Germany, as signor to the firm Hermann Frenkel, Molkau,

near Leipzig, Germany No Drawing. Application October 22. 1935, Se-

rial No. 46,209. In

10 Claims.

With coatings on wood disadvantages frequently occur, owing to the fact that the wood is not an unchangeable body, but is alive. The layers of coating, which are mostly relatively thin and also consist of organic bodies, are therefore also exposed in the dry state on one side to the influences of the surrounding atmosphere and on the other side to the influences of the wood lying under them. This has the disadvantage,

1 that coatings on wood are in general not very durable and become destroyed partly through deformations of the wood and partly through chemical and physical influence of the atmos phere.

With the object of improving the protection given to wood by coatings it has already been sought to shut off the wood from the atmosphere, most eifectively through first applying pore fillers, spattle and the like to the wood, and only then applying the usual film-forming painted-on coatings. Attempts have also been made to obtain more resistant coating films by using coating means which have to 'be dried in an oven. For this purpose, however, relatively high temperatures are necessary, to which the wood cannot be subjected, as otherwise it warps or becomes partly burnt. Hence with these known methods it has not been possible to obtain in a satisfactory manner resistant coatings on wood.

Now, it has been found that resistant coatings on wood are obtainable by thoroughly moistening the wood with a solution of a phenol-formaldehyde artificial resin which will harden at a low temperature and by then hardening the artificial resin at temperatures below 100 C. The process may for instance be carried out in such a manner that the wood, in the natural state or after'being dried or pressed in the usual way, is thoroughly moistened with a liquid, 30 to 70%, aqueous or alcoholic solution of a phenol-formaldehyde artificial resin which will harden at a low temperature and that the artificial resin is then hardened at temperatures of from 60 to 80 C. For this purpose the wood may be used either in the state in which it comes from the known drying and maturing processes, or it may previously be subjected to a heavy pressure up to about 20 atmospheres, in order, through a partial destruction of the cells, to check its natural show of life. According to -the invention the wood is first placed for several hours in a liquid, 30 to 70%, aqueous or alcoholic phenol-formaldehyde artificial resin, so that the wood becomes impregnated to a depth of about 2 mm. with the Germany January 31,

artificial resin solution. In order to hasten the penetration, this treatment may be carried out first in a vacuum and then under pressure. The wood thus impregnated with artificial resin is thereupon placed in a drying oven having a temperature of from 60 to 80 C. After about 1 to 12 hours a complete hardening of the artificial resin will have taken place, without the'wood having been damaged through the heating. The

wood now has a layer of artificial resin which.

has penetrated as far as 2 mm. and is intimately united with the wood fibres. The coating thus obtained is therefore firmly fixed on the surface of the wood, so that it cannot crack oil.

Ifthe gloss of the artificial resin layer on the surface of the wood should not yet sufiice, it can be increased by simple subsequent polishing or further layers of artificial resin, which are also hardened in the drying stove at 60 to 80 C., may be applied. In this way artificial resin layers up to a thickness of 1 mm. may be produced.

According to a modified form of the invention a extremely resistant coatings on wood may be obtained without any danger of damage to the latter, if a phenol-formaldehyde artificial resin varnish be used which dries and hardens at ordinary temperature in the air. These artificial resin varnishes, the best solvents for which are ethyl alcohol, methyl alcohol or acetone, have the property that, after being applied to the support, they harden when exposed to the air at an ordinary temperature to such an extent as to be dry and free from stickiness.

The hardening of these artificial resin varnishes when exposed to the air continues in the course of the next few days. This subsequent hardening process can be reduced to a few hours, if the coating which has been initially hardened by exposure to the air be subjected for a few hours to a temperature of about 40 to 80 C. By this means it is possible to obtain at the surface of the wooden article a layer of varnish which is hard, exceedingly resistant and has a high gloss. The thickness of the layer of varnish may be increased at will" by repeatedly painting the surface of the wood with the same artificial resin varnish.

It has also been found that the resistance of the highly glossy smooth varnish layers on wood may be further increased, if, before the application of the alcoholic phenol-formaldehyde artificial resin varnishes referred to above, the wood be treated with a pore filler which contains phenol-formaldehyde resin capable of hardening at ordinary temperature and filling substances and may contain solvents.

The pore filler may consist for instance of about 10 to 20% phenol-formaldehyde artificial resin capable of hardening at ordinary temperature, 0 to 30% solvents, for instance ethyl alcohol and if necessary alcohols having a higher boiling point and 60 to fillers. Suitable fillers are substances such as kaolin, bole, asbestos meal, asbestine, glass dust, slate meal, potato fiour, heavy spar, zinc white, white lead, iron oxide red, ochre and the like.

The wood is first treated with this pore filler. The filler is applied by being rubbed in with rags. The coating is then caused to dry and harden by being exposed to the air at ordinary temperature. The hardening of the pore filler may also take place at temperatures between 25 and 80 C., the time required for hardening being regulated according to the height of the temperature. By employing higher temperatures the time taken for hardening may be reduced to a few minutes.

Over this layer of pore filler an alcoholic artificial resin solution is then applied, which contains phenol-formaldehyde resin capable of hardening at ordinary temperature. This covering layer is preferably applied in a room the temperature of which is at least 20 C., for instance between 20 and 50 C., so that the applied layer of artificial resin very rapidly hardens. When the wood is to receive several covering layers, all these layers are applied under the same conditions. After the last covering has been applied, a further hardening of the layers of phenol formaldehyde artificial resin varnish may follow at temperatures up to 80 C.

The application of the alcoholic phenol formaldehyde artificial resin solution can be effected by immersion, painting-on, pouring-on or spraying-on.

It is frequently found that the surface of the layer of varnish, if the phenol formaldehyde resin is only dissolved in ethyl alcohol, becomes rippled and like the skin of an orange. By adding alcohols having a higher boiling point this disadvantage may be overcome. Suitable alcohols having a higher boiling point are those which boil between 80 and 150", such for instance as butyl alcohol, propyl alcohol and the like.

In the production of resistant coatings on wood a far better spread of the phenol formaldehyde artificial resin varnishes referred to above is obtained by adding to the phenol-formaldehyde artificial resin in accordance with a further modification of the invention varnish solutions of resins, more particularly fusible resins, such as colophony or shellac of artificial resins, such as vinyl resins. The resins or artificial resins used as additions are preferably dissolved in solvents that will also dissolve the phenol formaldehyde artificial resin. Such solvents are ethyl glycol, ethyl glycol acetate, ethyl alcohol, acetone and other ketones and alcohols having a higher boiling point, such for instance as butyl alcohol, propyl alcohol and the like. The quantity of added resins or artificial resins should amount to 2 to 50%, calculated on the phenol resin content of the phenol artificial resin varnish.

The addition of resins and artificial resins, such as colophony, shellac, vinyl resins and the like in amounts of from 2 to 50% to the phenol formaldehyde artificial resin is also suitable for pore fillers.

Through the addition of resins or artificial resins to the phenol formaldehyde artificial resin not only is a better spread of the layer of varnish obtained, but a quieter, smoother and glossier surface of the varnish coating.

If required, additional layers of varnish may be applied, cellulose derivative varnishes, oil varnishes and the like being employed.-

The coating produced in accordance with the invention is completely air-proof, extremely resistant tochemical influences, scratchproof, nonsensltive to blows and shocks and stable to temperatures up to about 200. As the wood can no longer be affected by any external influence, the natural show of life of the wood is as good as completely stopped. This provides the advantage that wood which has not been subjected to the usual drying will no longer sufi'er any deformations after it has been provided with a coating according to the invention. More particularly there will be no changes due to excretions of resin or to the sinking of the printed-on medium into the pores of the wood. The artificial resin covering produced in accordance with the invention is so intimately united with the body of the wood that the wood can be sewn, cut, drilled, planed, turned and operated on in any other way. The process according to the invention is therefore adapted to be employed with great advantage in the industry using ply-wood, that is for instance in the manufacture of furniture, radio apparatus, perambulators and the like. Owing to the very great hardness and resistance given to the wood by the artificial resin layer, this kind of treatment is particularly suitable for the laths of benches, for chair seats, table tops, wainscoting; for wood which is exposed to the action of the weather or of vapours or chemicals, which would attack it, an efi'ective and permanent protection is also provided.

To the phenol-formaldehyde artificial resin solutions used for soaking the wood dye-stuffs may be added for giving the coatings a suitable colouring.

The process according to the invention has the special advantage that with it perfectly clear colourless varnish coatings may be obtained without a detrimental covering of the artificial resins taking place. By this means more particularly highly glossy polishes on wooden panels, bench laths and the like may be produced. v

In place of the above pore fillers, spattles may be used, when it is a question of producing covering coating layers, which contain as the binding agent a phenol formaldehyde resin which will harden at ordinary temperature.

It has already been proposed to impregnate wood with artificial resin. For this purpose, however, it has hitherto always been the practice to employ hardening temperatures of from to This mode of operation has therefore not been able to attain any practical importance, as at the high hardening temperatures damage to the wood is unavoidable.

Examples 1. Condense under reflux 10 kg. phenol or cresol with 15 kg. formaldehyde and 100 g. dimethylamine. After the artificial resin has separated out, it is separated from the solution above it and is inspissated in a vacuum at temperatures up to 100 C. till it is of a viscous consistency. To this artificial resin is added, according to the desired content, ethyl alcohol or methyl alcohol or acetone as a solvent.

The artificial resin solution thus obtained is used for thoroughly moistening the wood, this being fol lowedby. the hardening process at 60 it ass umes-a viscous consistency and this insfpissated; ,ificial resin may then.be again brought n solution-with ethyl alcohol or methyl alcohol or acetone. The wood may then be lacquered withgthe resulting alcoholic artificial resin solutionvof any, desired resin content. In

' place of; 'NaQH. an: equivalent quantity of sodium atmospheric temperature.

bicarbonate o KOH may be used.

"Furthermore, in place of acetic acid phosphoric flCiQlqlfiQtlQ fifiid or phthalic acid may be used.

"3. -,Condense 10 kg. phenol with 10-50 kg. formaldehyde (30 per cent by weight), adding fromj 25 to-500 g. NaOH (solid). After the resin reaction or, the separating out of the resin the whole oithe mixture is inspissated in a vacuum at ,temperatures up to 100 C. until it assumes a .viscous -consistency. The alkaline resin is thereupon-dissolved in ethyl alcohol, methyl alcohol or acetone and in this solution is neutralized with inorganic or organic acids, such as hydrochloricacid, sulphuric acid, nitric acid, benzoic acid, phthalic acid, salicylic acid and the like,

or broughttoa slightly acid state. Such an alcoholic phenol-formaldehyde artificial resin solution has the-property of hardening at ordinary According to the composition of the phenol-formaldehyde artificial resin and the. nature and quantity of the added acids the time for hardening at ordinary temperature can be adjusted to take place in from 1 tog 24-' hours. By increasing the amount of added acid the hardening period is shortened and the hardening temperature is lowered or reduced down to the temperature of the air.

In place of sodium hydroxide an equivalent quantity of some other inorganic or organic base, for instance sodium bicarbonate, dimethylamine, may be used.

With this alcoholic artificial resin solution the wooden article is coated by painting on, spraying or immersion, whereupon the drying and hardening of the varnish is effected in the air at ordinary temperature. The coating of. varnish pro duced is remarkable for its great hardness and resisting capacity and for the high gloss.

These artificial resin varnishes may also be used for coating articles made of metal, glass or paper.

' 4. Condense 10 kg. phenol with -50 kg. formaldehyde (30 per cent by weight) adding from 25 to 500 g. NaOH. After completed reaction or a separation of the resin the entire mixture is inspissated in a vacuum at temperatures up to 100 C. till the consistency becomes viscous. The alkaline resin is dissolved in equal parts by weight of ethyl alcohol or alcohols having a higher boiling point and this alcoholic resin solution is then neutralized or acidulated with hydrochloric acid. The phenol formaldehyde resin solution (wood varnish) thus obtained has the property when applied to wood of forming a varnish-like coating which hardens of itself when exposed to the air. With the aid of this phenol formaldehyde resin solution the pore filler is prepared, which may have for instance the following composition:

.7 ,v enol resin solution is inspissatedi v a; vacuum at,temperatures up to 100 C. until hyde resin solution,

0-60 kg. solvent, such as ethyl alcohol or alcohols haying a higher boiling point,

60-90 filler, such as bole.

After t epore filler has been applied to the wood, the latter is coated for instance with a 50% alcoholic phenol formaldehyde resin solution. According to the purpose for which it is to be used the artificial resin content varies in the phenol formaldehyde resin solution between 25 and 75%.

It has been found that the best results are ob ained when in preparing the pore filler the same phenolvformaldehyde resin is used as in the subsequently applied covering layers, as in this case a firm binding between the pore filler and the covering layer is obtained.

5. Condense 10 kg. phenol with 20 kg. formaldehyde per cent by weight), adding 50 g. NaOH. After the reaction or separation of. the water has taken place, the entire mixture is inspissated in a vacuum at temperatures up to 100 C. until it has assumed a viscous consistency. The alkaline artificial resin is then dissolved with equal parts by weight of ethyl alcohol and is thereupon slightly acidulated with an alcoholic hydrochloric acid solution. To this alcoholic phenol formaldehyde solution are added 3 kg. of a 50% alcoholic shellac solution. resin varnish which is then ready for use is applied to the wood by printing, spraying or immersion. The hardening of the varnish layer takes place at room temperature or attemperatures of from to 80 C.

6. Condense 10 kg. cresol with 40 kg. formaldehyde (30 percent by weight), adding 100 g. NaOH, and inspissate in a vacuum until the consistency is viscous. This artificial resin is then diluted with a mixture of equal parts of ethyl glycol acetate and methyl alcohol, this mixture being used in a quantity corresponding to half the weight of the artificial resin. Slight acidulation is then efiected with an alcoholic sulphuric acid solution. resin solution are then added. The varnish is applied and dried as in Example 5.

What I claim:-

1. A process for producing resistant coatings on wood consisting in treating the wood with a varnish consisting of a solution in anorganic solvent of a hardenable phenol-formaldehyde resin obtained by alkali-condensing one mol. of phenol with at least 1.5 mols of formaldehyde, and thereupon hardening the resin on the wood at a temperature from normal to near but below 80 C.

2. A process for producing resistantcoatings on wood consisting in treating the wood with a varnish consisting of a solution in am organic solvent of a hardenable phenol-formaldehyde resin obtained by alkali-condensing one mol. of phenol with at least 1.5 mols of formaldehyde which varnish is neutralized by addition of an acid, and thereupon hardening the resin at a temperature from normal to not exceeding 80 C.

3. A process for producing resistant coatings on wood consisting in treating the wood with a varnish consisting of a solution in an organic solvent of a hardenable phenol-formaldehyde resin obtained by alkali-condensing one mol. of phenol with at least 1.5 mols of formaldehyde, which varnish is slightly acidified by an acid and thereupon hardening the resin at a temperature fromv normal to not exceeding 80 C.

10-30 kg. of a alcoholic phenolformalde- The 10 kg. of a 50% alcoholic vinyl.

4. A process for producing resistant coatings on wood consisting in treating the wood with a varnish consisting of a solution in an organic solvent of a hardenable phenol-formaldehyde resin obtained by alkali condensing one mol. of phenol with at least 1.5 mols of formaldehyde, which varnish is neutralized by addition of an acid, and thereupon hardening the resin in the air at ordinary temperature.

5. A process for producing resistant coatings on wood consisting in treating the wood with a varnish consisting of a solution in an organic solvent of a phenol-formaldehyde resin obtained by alkali condensing one mol. of phenol with at least 1.5 mols of formaldehyde, which varnish is slightly acidified by an acid, and thereupon hardening the resin in the air at ordinary temperature.

6. A process for producing resistant coatings on wood consisting in treating the wood with a varnish consisting of a solution in an organic solvent of a hardenable phenol-formaldehyde resin obtained by alkali condensing one mol. of phenol with at least 1.5 mols of formaldehyde, hardening the resin at a temperature from normal to near but below C., applying further layers of low temperature hardenable phenolformaldehyde resin, and hardening each applied layer at a temperature from normal to near but below 80 C. before applying the succeeding layer.

7. A process for producing resistant coatings on wood consisting in treating the wood with a pore filler comprising a hardenable phenol-formaldehyde resin obtained by alkali condensing one mol. of phenol withat least 1.5 mols oi. formaldehyde, hardening the resin oi the pore flller by subjection to temperatures from normal to near but not exceeding 80 C., applying a varnish consisting of a solution in an organic solvent of a phenol-formaldehyde resin obtained by alkali condensing one mol. of phenol ,with at least 1.5 mols of formaldehyde and thereupon hardening the resin at a temperature from normal to near but below 80 C.

8. A process for producing resistant coatings on wood, consisting in treating the wood with a pore filler comprising a hardenable phenol-formaldehyde resin obtained by alkali-condensing one mol. of phenol with at least 1.5 mols of formaldehyde, hardening the resin of the pore nller by subjection to temperatures from normal to near but not exceeding 80 C., applying a varnish consisting of a solution in an organic solvent of a phenol-formaldehyde resin obtained by alkali condensing one mol. of phenol with at least 1.5 mols of formaldehyde, which varnish is at least partially neutralized and thereupon hardening the resin in the air at ordinary temperature.

9. A process for producing resistant coatings on wood, consisting in treating the wood with a varnish consisting of a solution in an organic solvent of a hardenable phenol-formaldehyde resin obtained by alkali condensing one mol. of phenol with at least 1.5 mols of formaldehyde, thereupon hardening the resin at a temperature from normal to near but below 80 C. and applying over the resin coating a varnish layer selected from the group consisting of oil, and cellulose derivative varnish.

10. A process for producing resistant coatings on wood, consisting in treating wood with a varnish consisting of a solution in an organic solvent of a mixture of a hardenable phenol-formaldehyde resin obtained by alkali condensing one mol. of phenol with at least 1.5 mols of formalde- 1 hyde, together with an additional resin, and hardening the resin mixture at a temperature from normal to near but below 80 C.

WILHELM O'I'IO MAISCH. 

